Method and apparatus for manufacturing medium-walled and thin-walled seamless pipes

Abstract

A method of manufacturing seamless pipes having medium-thick or thin walls from an elongated hollow body of limited length which is reshaped by rolling to the desired final dimension, as well as a rolling apparatus for the carrying out of the method. This method of manufacturing seamless pipes having medium-thick or thin walls from an elongated hollow body is characterized by the fact that, with only one rolling pass the diameter of the hollow body is significantly reduced and by using an inner tool the inner surface is smoothed with only a slight change in wall thickness. Further, this method allows for the rolling of the axis of the hollow body to align with the axis of rolling. The rolling apparatus includes an inner tool which cooperates with two rolls to reduce the diameter of the pipe to a desired final dimension, the two rolls each having an inlet part, a feed part, a reducing part inclined at an angle within the range of more than 2° and up to 10° and adjoining same, with a transition in the form of a circular arc, and a substantially cylindrical reeler with a difference angle to the working part of the inner tool within the range of 0° to 1°, followed by an outlet part.

What is claimed is: 
     
       1. A method of manufacturing seamless pipes of medium-thick and thin walls from an elongated hollow body of limited length which is reshaped with a roll having a reeling part by rolling to the desired final dimension with only one rolling pass, said method comprising the steps of: significantly reducing the diameter of the hollow body with only slight change in wall thickness; and   reeling the inner surface of the hollow body with the use of an inner tool, said inner tool having a working part of greater length then the corresponding reeling part on the roll and being longitudinally displaceable relative to the hollow body and to said corresponding reeling part during at least a part of the rolling process so as to minimize material build up and disturbances.   
     
     
       2. The method according to claim 1 wherein, as seen in the direction of rolling, the entering hollow body is first reduced in diameter and directly thereupon the reeling of the inner surface takes place. 
     
     
       3. The method according to claim 1 wherein the inner tool is continuously displaced in longitudinal direction during the entire rolling process. 
     
     
       4. A method for the manufacture of seamless pipes of medium-thick and thin walls from a heated elongated hollow body which is reshaped by a roll having a reeling part with two successive different rolling methods to the desired final dimension and then cooled, comprising in a first rolling process with only one rolling pass, said method comprising the steps of: significantly reducing the diameter of the hollow body with only slight change in the wall thickness;   reeling the inner surface of the hollow body with the use of an inner tool, said inner tool being longitudinally displaceable during the rolling process so as to minimize material build up and disturbances, the axis of the hollow body being aligned during the rolling with the axis of rolling; and   calibrating the hollow body to the desired final dimensions in a second rolling process.   
     
     
       5. A rolling device, comprising a piercing rolling mill having two rolls which are driven in the same direction and have an inlet part and an outlet part and are inclined by a transport angle to the axis of rolling and a guide arranged in a plane turned 90° from the rolling plane and an inner tool fastened to a holding bar and having a working part, wherein, as seen in the direction of rolling, each of the rolls has a feed part for feeding a hollow body which is followed by a reducing part with a reduction angle within the range of more than 2° up to 10°, with a transition in the form of a circular arc between said reducing part and a cylindrical reeler part, the cylindrical reeler part having a difference angle to the working part of the inner tool within the range of 0° to 1.0°, which is followed then by an outlet part for rounding, and wherein the guide has two fixed guide straight-edges which lie opposite each other and the working part of the inner tool has a greater length than the reeling part of the rolls, wherein, seen in the direction of rolling, the starting end of the working part of the inner tool lies in front of the start of the reeling part of the rolls, with said inner tool being longitudinally displaceable relative to the hollow body and to the corresponding reeler part on said roll during at least part of the rolling process so as to minimize material build up and disturbances. 
     
     
       6. The rolling device according to claim 5, wherein the angle of reduction in the reducing part of the rolls is 3°-5°. 
     
     
       7. The rolling device according to claim 5, wherein as seen in the direction of rolling, the feed part has a feed angle of about 1° and is arranged in front of the reducing part. 
     
     
       8. The rolling device according to claim 5, wherein the axes of the rolls have a spread angle with respect to the axis of rolling. 
     
     
       9. The rolling device according to claim 8, wherein the point of intersection of the axes of the rolls with the rolling axis, seen in the rolling direction, lies behind the rolling mill. 
     
     
       10. The rolling device according to claim 9, wherein the size of the spread angle is so selected that for the average diameter of a predetermined range of dimensions in the reducing part the circumferential speed of the rolls decreases proportionally to the decrease in the diameter of the hollow body. 
     
     
       11. The rolling device according to claim 5, wherein the inner tool, in addition to the cylindrical working part, further comprises, a conically developed section, which is designed to rest against the inner surface of the hollow body to be rolled only during the final or initial rolling and the cone angle of which is substantially equal to the reduction angle of the rolls. 
     
     
       12. The rolling device according to claim 11, wherein the working part of the inner tool for the reeling has a continuation in the direction opposite the direction of rolling, the continuation extending over half the length of the reducing part of the roll which is adjoined, with a rounded shoulder, by a convergently conically developed initial rolling part which is designed so that during the rolling, the initial rolling part rests against the inner surface of the entering hollow body and the cone angle of which is substantially equal to the reduction angle and which extends up into the initial region of the reducing part.